In the field of rendering web page content, structured data that defines the content of a web page can be syntactically and logically separated from a set of presentation semantics that define the visual appearance and layout of the web page. Such a separation has the advantage that one version of the content can be optimized for presentation on various different types of media devices by using different presentation semantics. Some of the presentation semantics describe how the content should be laid out for a particular type of media device. For example, using different presentation semantics, the same content can be laid out in a large format for a personal computer (PC) with a relatively large display, a small format for a smartphone with a relatively small display, and a medium format for an automobile infotainment system or a tablet computer. Some techniques exist for automatically determining the appropriate layout of the web page based on the type of media device on which the web page is being rendered or on the size of the viewport or display window within the web browser of the media device.